The NASA InSight mission, landing in late November 2018, promises to revolutionize our understanding of Martian interior structure via analysis of seismic data returned by the SEIS instrument. The extent to which the mission’s potential is realized will depend on the number of detectable seismic events that occur during the period of operation. Here I estimate the rate of detectable events generated by volcano-tectonic activity on Mars based on extrapolation of Hawai’i’s seismic record. I use a catalog of 5603 earthquakes spanning 48 years [IRIS, 2018], with moment magnitudes MW ranging from 3.0 to 6.9, to derive the Gutenberg-Richter (G-R) frequency-magnitude relation for the Island of Hawai’i, expressed as log(N) = a – b MW, where N is the number of earthquakes with magnitudes greater than or equal to MW, and a and b are constants. By this analysis, one earthquake with MW 5.1 or greater can be expected every year at Hawai’i. Under the assumption that the mechanisms of seismicity associated with edifice building are similar at Hawai’i and Olympus Mons (supported by observation of decollement-based volcanic spreading at both), I use the same b for both settings and scale a according to estimates of magmatic volume flux rates dV/dt at both settings. Over the 80 Myr history of the Hawaiian-Emperor volcanic chain, dV/dt ≈ 1.7 x 10-2 km3/yr. An estimate of dV/dt for the Olympus Mons volcano on Mars was derived from paleotopographic analysis of a set of lava flows south of Olympus Mons with discordant topography. Given the mean flow age from crater counts (210 Ma), an estimate of the amount of volcanic material needed to cause deflections of flow orientations of the required magnitudes yields estimates of dV/dt over this timespan ranging from 6.33 x 10-4 to 6.43 x 10-3 km3/s. Taking the mean of these values and scaling a by the ratio of dV/dt values for Mars and Hawai’i yields a rate of at least 1 quake of MW = 4.4 or greater per year (Figure 1). Thus, under several assumptions (including a steady recent magma supply rate for Olympus Mons), we can expect ≈ 2 volcano-tectonically driven quakes of magnitude MW > 4.4 from the vicinity of Olympus Mons during the nominal 2 Earth-year InSight prime mission. This is a conservative lower bound that does not consider contributions from numerous potential volcano-tectonic sources in Tharsis and elsewhere on Mars.

Sputnik Planitia on Pluto is a vast plain consisting of a nitrogen ice deposit filling a broad topographic depression, likely an impact basin. The basin displays a broad, raised rim and is surrounded by numerous extensional fracture systems, each with characteristic orientations with respect to the basin center. The nitrogen ice exerts a large mechanical load on the water ice outer shell crust (here also containing the lithosphere). We calculate models of stress and deformation related to this load, varying dimensional, mechanical, and boundary condition properties of the load and Pluto’s lithosphere, in order to constrain the conditions that led to the formation of the observed tectonic and topographic signals. We demonstrate that the tectonic configuration is diagnostic of a particular set of conditions that hold for the Sputnik basin and Pluto, including moderate elastic lithosphere thickness (50 ± 10 km) and a wide load set into a basin that was pan-shaped and shallow (~3 km) at the time of nitrogen deposition initiation. These tectonic systems show the contributions of both flexural (bending) and membrane (stretching) responses of the lithosphere, with the latter dominating in proportion to the importance of spherical geometry effects (i.e., wide loads). Rim topography may also show an influence of primordial annular trans-basin ice shell thickening from the impact process. Analysis of stress-driven cryomagma transport shows that loading stresses can facilitate ascent of cryomagmas in annular zones around the basin, the locations of which overlap the observed distances from Sputnik of several candidate cryovolcanic sites.